Summary: Following successful agrobacterial transformation, target recombinant proteins, such as antibodies, vaccines, and enzymes can be expressed in high amount within the plant system. Comparing to the traditional bacterial, yeast, or mammalian expression systems, the plant expression system has the advantages of higher protein yield, lower cost, shorter turn-over time and increased safety. Among all plant species, the lettuce transient expression system is considered as the most promising system for the expression of recombinant proteins.